Create a new String Type. 
All string types must include an encoding.
- Resource Management:
 - This function allocates resources that must later be freed by calling DOFType_Destroy.
 
- Parameters
 - 
  
    | encoding | The MIBenum value, a unique value identifying a specific coded character set used by all strings in val. This should be > 2. Example: DOFVALUESTRING_US_ASCII.  | 
    | length | Maximum string length, in characters (not necessarily byte size). | 
  
   
- Returns
 - The new DOFType, or NULL if it could not be created.